One of the most demanding aspects of a display system is its need to operate in real time. A display system must respond to an input data stream over which it has little or no control and must be capable of displaying information at a frame rate that is at least as fast as that input, if not faster. For progressive HDTV display, this can be up to 60 frames of 1920×1080 pixel data per second. Display systems capable of displaying full-resolution image frames from such an input must be capable of driving 2,073,600 pixels every 16.667msec. If the display system uses a full-frame spatial light modulator (SLM) such as Texas Instrument's Digital Micromirror Device™ (DMD), each pixel in the image can use the full 16.667msec to render its intensity level. For digital SLMs, a common method for rendering different intensity levels is to use pulse width modulation (PWM). A system using PWM divides up a fixed time interval, such as the frame refresh rate, into smaller blocks during which time the device is turned on and off. The eye integrates these on and off times to form an intermediate intensity level often referred to as grayscale. Studies have demonstrated (see for example, “Grayscale Transformations of Cineon Digital Film Data for Display, conversion, and Film Recording,” v 1.1, Apr. 12, 1993, cinesite Digital Film Center, Hollywood, Calif.) that for true cinema-grade digital display systems, 14-bits of linear data are required to render the appropriate grayscale levels in an image. At a refresh rate of 60 frames per second, a display system using a full-frame or area array SLM requires a PWM clock frequency of approximately 1 MHz, a very realizable goal.
However, display systems employing linear array SLMs such as the conformal grating device detailed by Marek W. Kowarz in U.S. Pat. No. 6,307,663, issued Oct. 23, 2001, titled “Spatial Light Modulator With Conformal Grating Device,” are much more demanding. For progressive HDTV display systems using linear array SLMs, each pixel has at most 1/1920th of the source data frame rate during which time it must render the required intensity level. In fact, display systems using linear array SLMs are even more demanding as they must accommodate the overhead necessary for the scanning system to recover before displaying the next frame of data. For example, a scanning linear array SLM digital display system that has a 20% recovery time would require a PWM processing clock of approximately 2.4 GHz to render the required 14-bits of linear grayscale data. While a small handful of very specialized integrated circuits are capable of operating at such frequencies, most realizable systems are unable to operate at such high clock rates. There is a need, therefore, for high-speed PWM architectures for scanned linear array SLM display systems that can operate at speeds in excess of 1 GHz using currently available technology.